Optical waveguide element, optical modulation device using the same, and optical transmission device

Abstract

To provide an optical waveguide element that suppresses discharges between electrodes on either side of the optical waveguide. [Solution] An optical waveguide element having a substrate 1 having a pyroelectric effect, a projection P2 extending in a specific direction formed on the surface of the substrate, and an electrode EL covering at least a part of the projection, characterized in that the charges generated by the pyroelectric effect on each of the two sides of the projection P2 are opposite in positive and negative charges (+EC, -EC), and the electrode EL is arranged to cover the two sides of the projection P2 in each electrically connected region.

Description

Technical Field

[0001] The present invention relates to an optical waveguide element, an optical modulation device using the same, and an optical transmission device, and particularly relates to an optical waveguide element having a substrate with a pyroelectric effect, a protrusion extending in a specific direction formed on the surface of the substrate, and an electrode covering at least a part of the protrusion.

Background Art

[0002] In the fields of optical measurement technology and optical communication technology, optical waveguide elements such as optical modulators using a ferroelectric material such as lithium niobate (LN) as a substrate are widely used. In a substrate using a ferroelectric material, due to a change in temperature, the polarization of the dielectric changes, and a so-called pyroelectric effect occurs where the charge distribution generated on the substrate surface changes.

[0003] On the other hand, in an optical waveguide element, in order to reduce the driving voltage and miniaturize, the optical waveguide formed on a ferroelectric substrate is made into a rib-type optical waveguide, and the height and width of the cross-section of the rib-type optical waveguide are reduced to, for example, 1 μm or less. Moreover, in order to increase the strength of the electric field applied to the optical waveguide, the distance between the electrodes is also configured to be as narrow as several μm. As an example, Patent Document 1 shows an X-cut type LN substrate provided with a rib-type optical waveguide.

[0004] For example, when a rib-type optical waveguide is formed on the surface of an X-cut type LN substrate, as shown in FIG. 1, a protrusion P1 forming the rib-type optical waveguide OW and two protrusions P2 sandwiching the optical waveguide are formed. Then, depending on the direction in which the optical waveguide OW extends, charges due to the pyroelectric effect are generated on the side surfaces of the protrusions P1 and P2. FIG. 1 shows a state where positive charges (+EC) are generated on the right side surface of the protrusion shown in the drawing, and negative charges (-EC) are generated on the left side surface. In the X-cut type LN substrate, the side surface of this protrusion is the Z plane.

[0005] Also, in an optical waveguide element using an X-cut type LN substrate, in the acting part for applying an electric field to the rib-type optical waveguide, in order to effectively change the refractive index of the optical waveguide with respect to the applied electric field, this Z plane is usually arranged on the side surface of the optical waveguide. In Figure 1, the positive and negative signs of the charges generated at the protrusions (P1, P2) are shown for convenience, but the sign of the charges generated on the sides of the protrusions will appear differently depending on whether the temperature is rising or falling.

[0006] The electrodes EL that apply an electric field to the optical waveguide OW are positioned close to the rib-type optical waveguide OW, so that a portion of the electrodes EL covers one side of the protrusion P2. As described above, the spacing between the electrodes EL on either side of the optical waveguide becomes narrower due to the reduction in driving voltage and miniaturization of the optical waveguide element. Therefore, due to the manufacturing process of the optical waveguide element and temperature changes during operation, the charge on the side of the protrusion P2 generated by the pyroelectric effect appears on the surface of the electrode EL covering that side, causing a discharge phenomenon ED between the electrodes EL covering sides with different surface charges, as shown in Figure 1.

[0007] The instantaneous large currents that occur during a discharge phenomenon (ED) can destroy the optical waveguide between the electrodes. Even if a discharge phenomenon does not occur, the electric field strength between the electrodes increases, which can cause local polarization reversal in the ferroelectric material that makes up the optical waveguide. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2022-142650 [Overview of the project] [Problems that the invention aims to solve]

[0009] The problem that this invention aims to solve is to provide an optical waveguide element that solves the above-mentioned problems and suppresses discharges between electrodes on either side of the optical waveguide. Furthermore, it aims to provide an optical modulation device and an optical transmission device using this optical waveguide element. [Means for solving the problem]

[0010] To solve the above problems, the optical waveguide element, optical modulation device using the same, and optical transmission device of the present invention have the following technical features. (1) An optical waveguide element having a substrate having a pyroelectric effect, a projection extending in a specific direction formed on the surface of the substrate, and an electrode covering at least a part of the projection, characterized in that the charges generated by the pyroelectric effect on each of the two sides of the projection are opposite in positive and negative charges, and the electrode is arranged to cover the two sides of the projection in each electrically connected region.

[0011] (2) The optical waveguide element described in (1) above is characterized in that a plurality of protrusions are formed on the substrate, some of which are optical waveguides, and the electrodes are electrodes for applying an electric field to the optical waveguide.

[0012] (3) In the optical waveguide element described in (1) above, the electrode has a lower electrode that is in contact with the surface of the substrate and an upper electrode that is positioned above the lower electrode, and each lower electrode is positioned so as to cover the two sides of the protrusion.

[0013] (4) In the optical waveguide element described in (1) above, a resistivity of 10 is provided, including the space between the substrate and the electrode and covering the upper surface of the substrate, or including the upper side of the electrode and covering the upper surface of the substrate. 6 ~10 11 It is characterized by the placement of a conductive film with a density of Ωm.

[0014] (5) In the optical waveguide element described in (1) above, the electrode is characterized in that, in each electrically connected region, the ratio of the area covering one side of the protrusion to the area covering the other side is within the range of 0.8 to 1.2.

[0015] (6) The optical waveguide element described in (1) above is characterized in that the angle of the side surface of the projection with respect to a plane parallel to the surface of the substrate is less than 75 degrees.

[0016] (7) In the optical waveguide device according to (1) above, a plurality of protrusions are formed on the substrate, the protrusions having an interval between adjacent protrusions in the range of 1 to 20 μm, and the electrode being disposed on at least one of the adjacent protrusions.

[0017] (8) In the optical waveguide device according to (1) above, the thickness of the electrode disposed on the side surface of the protrusion is thinner than the thickness of the electrode disposed on the top of the protrusion.

[0018] (9) The optical waveguide device according to (2) above is an optical modulation device, characterized in that the optical waveguide device is housed in a housing and includes an optical fiber for inputting or outputting light waves to or from the optical waveguide.

[0019] (10) In the optical modulation device according to (9) above, the optical waveguide device includes a modulation electrode for modulating light waves propagating through the optical waveguide, and an electronic circuit for amplifying a modulation signal input to the modulation electrode of the optical waveguide device is provided inside the housing.

[0020] (11) An optical transmission device, characterized by comprising the optical modulation device according to (9) above and an electronic circuit for outputting a modulation signal for causing the optical modulation device to perform a modulation operation.

Advantages of the Invention

[0021] In an optical waveguide device having a substrate having a pyroelectric effect, protrusions extending in a specific direction formed on the surface of the substrate, and an electrode covering at least a part of the protrusions, on each of two side surfaces of the protrusions, charges generated by the pyroelectric effect are opposite in positive and negative to each other, and the electrode is disposed so as to cover the two side surfaces of the protrusion in each electrically connected region, so that the charges generated on the side surfaces of the protrusion can be neutralized, and it is possible to suppress a discharge phenomenon or the like occurring between the electrodes. Furthermore, it is also possible to provide an optical modulation device and an optical transmission device using an optical waveguide device in which a discharge phenomenon or the like is suppressed.

Brief Description of the Drawings

[0022] [Figure 1] It is a cross-sectional view showing a conventional optical waveguide device. [Figure 2] It is a cross-sectional view showing a first embodiment of the optical waveguide device according to the present invention. [Figure 3] It is a plan view showing a second embodiment of the optical waveguide device according to the present invention. [Figure 4] It is a cross-sectional view taken along the dashed-dotted line A - A' in FIG. 3. [Figure 5] It is a plan view showing a third embodiment of the optical waveguide device according to the present invention. [Figure 6] It is a cross-sectional view taken along the dashed-dotted line A - A' in FIG. 5. [Figure 7] It is a cross-sectional view showing a fourth embodiment of the optical waveguide device according to the present invention. [Figure 8] It is a cross-sectional view showing a fifth embodiment (part 1) of the optical waveguide device according to the present invention. [Figure 9] It is a cross-sectional view showing a fifth embodiment (part 2) of the optical waveguide device according to the present invention. [Figure 10] It is a plan view showing a sixth embodiment of the optical waveguide device according to the present invention. [Figure 11] It is a cross-sectional view taken along the dashed-dotted lines A - A' and B - B' in FIG. 10. [Figure 12] It is a plan view showing a seventh embodiment of the optical waveguide device according to the present invention. [Figure 13] It is a cross-sectional view showing an eighth embodiment of the optical waveguide device according to the present invention. [Figure 14] It is a plan view for explaining the optical modulation device and the optical transmission device of the present invention.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, the optical waveguide device of the present invention will be described in detail using preferred examples. As shown in Figure 2, the present invention relates to an optical waveguide element having a substrate 1 having a pyroelectric effect, a projection P2 extending in a specific direction formed on the surface of the substrate, and an electrode EL covering at least a part of the projection, characterized in that the charges generated by the pyroelectric effect on each of the two sides of the projection P2 are opposite in positive and negative charges (+EC, -EC), and the electrode EL is arranged to cover the two sides of the projection P2 in each electrically connected region.

[0024] The material of the pyroelectric effect substrate 1 used in the optical waveguide element of the present invention is a ferroelectric substrate. Specifically, substrates such as lithium niobate (LN), lithium tantalate (LT), PLZT (lead zirconate lanthanum), and magnesium-doped substrates of these substrate materials can be used. Vapor-grown films made from these materials can also be used. Figure 2 shows an example of an X-cut LN substrate, where the side surface of the protrusion P2 is the Z-plane.

[0025] On the surface of the pyroelectric substrate 1, protrusions P1 are formed as optical waveguides, constituting a rib-type optical waveguide OW. Electrodes EL are formed so as to sandwich the rib-type optical waveguide OW in order to apply an electric field based on a modulation signal or DC bias to the optical waveguide OW. To achieve velocity matching between the microwave and optical waves of the modulation signal, the thickness of the substrate 1 forming the optical waveguide can be set to 10 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less. To increase the mechanical strength of such a thin substrate 1, a holding substrate SS may be bonded and fixed to the underside of the substrate 1 either by direct bonding or via an adhesive layer AD such as resin. As the holding substrate SS to be directly bonded, materials with a lower refractive index than the optical waveguide or the substrate on which the optical waveguide is formed, and with a similar coefficient of thermal expansion to the optical waveguide, such as alkali-free glass or a substrate containing an oxide layer of quartz, are preferably used. Composite substrates with a silicon oxide layer formed on a silicon substrate (abbreviated as SOI or LNOI) or a composite substrate with a silicon oxide layer formed on an LN substrate can also be used. When using such a composite substrate, it is possible to omit the bonding layer AD.

[0026] As a method for forming the optical waveguide OW, as shown in Figure 2, it is possible to use a rib-type optical waveguide in which the portion corresponding to the optical waveguide is a protrusion on the substrate, such as by etching the substrate 1 or forming grooves on both sides of the optical waveguide. When using the thin plate substrate described above, the height of the rib-type optical waveguide is set to 4 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less or 0.4 μm or less. The width of the rib-type optical waveguide OW is also set to a width of, for example, 1 μm or less, similar to the height. It is also possible to form a vapor-deposited film on the holding substrate SS and process the film into the shape of an optical waveguide.

[0027] In optical waveguide elements to which the present invention is applied, as shown in Figure 2, when a projection P2 extending in a specific direction is formed on a substrate 1 having a pyroelectric effect, charges with opposite positive and negative charges (+EC, -EC) may be generated on the two sides of the projection P2 due to the pyroelectric effect. Specifically, when an X-cut LN substrate is used, if the direction of formation of the projection is selected so that the side of the projection P2 is the Z-plane, then charges with opposite positive and negative charges will be generated on the two sides of the projection P2 due to the pyroelectric effect.

[0028] In this invention, electrodes are positioned to cover the sides of protrusions that generate different positive and negative charges, and the shape of the electrodes is formed so that the electrodes positioned on different sides are electrically connected. This creates an effect at the electrode EL that cancels out (cancels out) the charges generated on the sides of the protrusions. In this way, the region in which one electrode EL is formed is always set to include each of the sides of the protrusions where different charges are generated.

[0029] As a result, even if a pyroelectric effect occurs, the electrodes EL on both sides of the rib-type optical waveguide OW will not acquire either a positive or negative charge, and no potential difference will be generated between the electrodes EL. Therefore, the optical waveguide will not be destroyed by discharge phenomena or the like.

[0030] Figure 3 is a plan view showing an example of an optical waveguide element using an optical waveguide in which multiple Mach-Zehnder type optical waveguides are arranged in a nested manner as a rib-type optical waveguide OW. Figure 4 shows a cross-sectional view along the dashed line A-A' in Figure 3. A projection P1 constituting the optical waveguide OW is formed on the surface of the substrate 1, and projections P21 and P22 are formed on either side of it. Similar to Figure 2, positive and negative charges are generated on the two sides of projections P21 and P22 due to the pyroelectric effect, so electrodes EL1 and EL2 are placed on all projections (P21, P22) except for the rib-type optical waveguide OW. Each electrode EL1 or EL2 is configured to cover both sides of the projection that generate different charges (the side that generates a positive charge (+EC) and the side that generates a negative charge (-EC) in Figure 2).

[0031] When electrodes with suppressed charge (EL1 and EL2) are placed next to each other, the potential difference between these adjacent electrodes becomes smaller, and as a result, discharge breakdown can be suppressed. As shown in Figures 3 and 4, when multiple protrusions are formed on the substrate 1, there are many protrusions where the distance between adjacent protrusions is in the range of 1 to 20 μm, making discharge breakdown more likely to occur. For this reason, by placing electrodes that cover both sides of at least one of the adjacent protrusions, it is possible to suppress discharge breakdown.

[0032] Figure 5 shows the electrode arrangement when a differential signal is applied to a single Mach-Zehnder optical waveguide. Specifically, if electrode EL1 is the positive electrode to which a positive electrical signal is applied, then the electrode (EL21) that sandwiches the optical waveguide OW together with the positive electrode EL1 becomes the negative electrode to which a negative electrical signal is applied. The electrode sandwiched between the two Mach-Zehnder optical waveguides is divided into three electrodes, forming the negative electrode EL21, the ground electrode EL22, and the negative electrode EL23. An example of an electrode arrangement sandwiching the two branch waveguides (OW) of a single Mach-Zehnder optical waveguide is the arrangement in the order of ground electrode - negative electrode - branch waveguide OW - positive waveguide - branch waveguide OW - negative waveguide - ground electrode.

[0033] Normally, since the electrode EL2 in Figure 3 is simply divided into three, a configuration that subdivides only the electrode into three is sufficient. However, when the electrode EL2 in Figure 4 is divided into three, the electrodes at both ends are connected to one side of the projection P22, while the central electrode is positioned only on the top surface of the projection P22. In such a case, a potential difference is generated between the electrodes positioned on both sides of the projection P22, which could lead to discharge breakdown.

[0034] In the optical waveguide element of the present invention, when such a differential signal is applied, as shown in Figure 6, a dummy groove DM is added between adjacent Mach-Zehnder type optical waveguides, and the electrodes are formed in each of the three divided electrodes (EL21~23) so as to cover both sides of the protrusions (P221~P223), thereby suppressing discharge breakdown.

[0035] Figure 7 shows an example of an optical waveguide element in which electrodes are configured in multiple stages, such as thin electrodes (ELL1, etc.) and thick electrodes (ELU1, etc.). The intention behind configuring electrodes in multiple stages in this way is that the electrodes closest to the optical waveguide are thin electrodes placed at a height close to the optical waveguide in order to efficiently generate an electric field in accordance with the height of the optical waveguide. Furthermore, in electrodes that propagate microwaves such as modulated signals, thick electrodes are formed on top of thin electrodes in order to match the effective refractive index of light with the refractive index (Nm) of microwaves and to reduce the waveguide loss of the electrodes.

[0036] Since the thin electrodes (ELL1, etc.) and thick electrodes (ELU1, etc.) are electrically connected to each other, it is possible to configure them such that, for example, the thin electrodes cover the positively charged side of the protrusion and the thick electrodes cover the negatively charged side of the protrusion. However, in Figure 7, the thin electrodes (ELL1, ELL21, ELL22) are first configured to cover two sides of the protrusion, so as not to create a large potential difference between the thin electrodes. This is to suppress the occurrence of discharge breakdown between the thin electrodes due to the change in substrate temperature between the formation of the thin electrodes and the formation of the thick electrodes, which can cause a pyroelectric effect.

[0037] Figures 8 and 9 show a slightly conductive film CF formed on the substrate 1 or on the electrodes (EL1-2) to further reduce the potential difference between each electrode. Specifically, an electric field corresponding to the modulation signal and DC bias is formed between each electrode and applied to the optical waveguide. Therefore, it is not possible to form a conductive film connecting the electrodes, but in order to mitigate the potential difference generated by the pyroelectric effect as much as possible, a film with an electrical resistivity of 10 6 ~10 11 A film with a slight conductivity of Ωm is formed. Si and SiN can be used as the film CF. By forming this slightly conductive film, even if a potential difference occurs between the electrodes, discharge breakdown can be suppressed by gradual discharge.

[0038] In Figure 8, the film CF is formed after the electrodes are formed, so it includes the area above the electrodes and covers the upper surface of the substrate 1. In other words, after forming protrusions such as optical waveguides (P1, P21, and P22) on the substrate 1, the electrodes (EL1, EL2) are formed, and then the film CF is formed over the entire upper surface of the substrate 1. Of course, it is also possible to form the film partially, including protrusions where electrodes have not been formed, so that each electrode is connected.

[0039] On the other hand, in Figure 9, after forming protrusions (P1, P21, and P22) on the substrate 1, the film CF is placed over the entire upper surface of the substrate 1 before forming the electrodes. Then, the electrodes (EL1, EL2) are formed. As a result, the film CF is positioned to cover the upper surface of the substrate 1, including the space between the substrate 1 and the electrodes. In Figure 9, it is also possible to partially position the film CF, including at least the protrusions where electrodes are not formed, to connect each electrode, rather than forming it over the entire upper surface of the substrate 1.

[0040] Figures 10 and 11 illustrate how to handle cases where the area of ​​the sides on both sides of the protrusion is different. Figure 10 is a plan view of the optical waveguide element, and Figure 11 is a cross-sectional view along the dashed lines A-A' and B-B' in Figure 10. Figure 11(a) corresponds to the dashed line A-A', and Figure 11(b) corresponds to the dashed line B-B'.

[0041] Looking at Figure 11, at projection P22, the lengths (areas) of the sides on both sides of the projection are the same, but at projection P21 (the leftmost part of the drawing), the length (area) of the left side of the projection is larger than the length (area) of the right side. The projections at both ends of Figure 11 have different lengths (areas) of the sides on both sides. The difference in the lengths (areas) of the sides of the projection can also be expressed as having different groove depths on both sides of the projection.

[0042] Therefore, as shown in Figures 10 and 11, for the electrode EL1 covering the protrusion P21, a portion EM is provided that is not partially covered by the electrode on the electrode with the longer (larger) side length (area) of the protrusion. It is preferable to set the area of ​​the side of the protrusion covered by one electrode EL1 to be approximately the same for each different side of the protrusion. This makes it possible for a single electrode to cancel out (cancel out) the positive and negative charges generated by the pyroelectric effect.

[0043] Focusing on the formation region of one electrode that partially covers the protrusion, it is preferable that the ratio of the area covering one side of the protrusion (e.g., the side that generates a positive charge +EC) to the area covering the other side (e.g., the side that generates a negative charge -EC) is equal. However, if this ratio is within the range of 0.8 to 1.2, it is possible to suppress the charge accumulated on the electrode to some extent, thereby suppressing discharge breakdown.

[0044] Figure 12 shows a state in which the region of a single electrode EL3 is formed spanning multiple protrusions (P30~P32). Even in such a case, it is preferable to set the sum of the area covered by the electrode (e.g., EL32) on the side surface of the protrusion where a positive charge (+EC) is formed and the sum of the areas covered by the electrodes (e.g., EL30, EL31) on the side surface of the protrusion where a negative charge (-EC) is formed to be approximately the same, so that the positive and negative charges cancel each other out overall. However, even in this case, it is possible to suppress discharge breakdown to some extent by setting the ratio of the area covered by the electrode on the positively charged side to the area covered by the electrode on the negatively charged side in the range of 0.8 to 1.2. In this way, by arranging a single electrode spanning multiple protrusions, the charging due to the pyroelectric effect can be canceled in a limited space, and design flexibility can also be ensured.

[0045] Figure 13 shows an electrode EL covering a single protrusion P. It is preferable that the thickness EH2 of the electrode placed on the side of the protrusion P is thinner than the thickness EH1 of the electrode placed on the top of the protrusion P. For example, in the case of an X-cut LN substrate, the side of the protrusion P is the Z-plane, and the Z-plane is subjected to stress due to the difference in the coefficient of thermal expansion of the materials, and is prone to static charge when subjected to stress. To prevent this static charge, it is preferable that the electrode thickness on the Z-plane be thinner than the electrode placed on the X-plane (top of the protrusion). More specifically, the thickness EH1 of the electrode on the top of the protrusion is set to 200 nm or more, and the thickness EH2 of the electrode on the side of the protrusion is set to EH1 × 0.8 or less.

[0046] For example, the coefficients of linear expansion in the X and Y directions of the Z plane of an LN substrate are both 1.5 × 10⁻⁶. -5 ( / K), and the coefficient of linear expansion in the Y and Z directions of the X plane is 1.5 × 10 in the Y direction. -5 ( / K) and the Z direction is 0.75 × 10 -5 The coefficient of thermal expansion of the electrode material (Au) is 1.4 × 10⁻⁶. -5 ( / K) The stress at the interface of dissimilar materials is the product of the difference in the coefficients of thermal expansion of the two materials and the length of the contact surface. Since the length in the Z direction (left-right direction in the drawing) is sufficiently smaller than the length in the Y direction (perpendicular direction in Figure 13), the stress due to the difference in the coefficients of thermal expansion of the electrode in the Z direction is extremely small. If the electrode thicknesses of the Z and X planes are the same, the stress due to the difference in the coefficients of thermal expansion of the Z and X planes can be said to be approximately equal. However, since the Z plane is more prone to charging due to stress than the X plane, it is possible to reduce stress and suppress charging by making the electrode thickness of the Z plane thinner than that of the X plane.

[0047] In order to reliably form electrodes on the sides of the protrusions, and to make the thickness of the electrodes on the sides of the protrusions thinner than the electrodes on the top of the protrusions, it is preferable that the angle θ of the side of the protrusion P with respect to the plane parallel to the surface of the substrate 1 in Figure 13 is less than 75 degrees. Furthermore, it is preferable that the angle θ is greater than 45 degrees. This is because, in the present invention, in order to more significantly exhibit the effect of the configuration in which both sides (Z planes) of the protrusion in Figure 13 are covered with electrodes, it is considered preferable that the side angle of the protrusion's side is greater than the X plane component. As the side angle θ of the protrusion decreases, the influence of the Z plane (ease of charging) decreases, so it is preferable to set the angle θ to be greater than 45 degrees so that the influence of the Z plane remains more.

[0048] Next, we will describe examples of applying the optical waveguide element of the present invention to optical modulation devices and optical transmitting devices. Figure 14 illustrates an optical modulation device incorporating an optical waveguide element using a nested type optical waveguide, but the present invention is not limited to this and can also be applied to optical phase modulators, optical modulators with polarization combining functions, optical waveguide elements integrating more Mach-Zehnder type optical waveguides, bonding devices with optical waveguide elements made of other materials such as silicon, and devices for sensor applications. Furthermore, it goes without saying that it can also be applied to high-bandwidth-coherent driver modulators (HB-CDM).

[0049] As shown in Figure 14, the optical waveguide element has an optical waveguide OW formed on a substrate 1 and a modulation electrode (not shown) that modulates the light wave propagating through the optical waveguide, and is housed in a housing CA. Furthermore, by providing an optical fiber (F) that inputs and outputs light waves to the optical waveguide, an optical modulation device MD can be constructed. The optical fiber F is optically coupled to the optical waveguide OW in the optical waveguide element using an optical block or lens barrel equipped with an optical lens. However, the optical fiber may be introduced into the housing through a through-hole penetrating the side wall of the housing, and the optical fiber may be directly joined to an optical component or substrate, or an optical fiber with a lens function at its end may be optically coupled to the optical waveguide in the optical waveguide element. L1 represents incident light, and L2 represents outgoing light.

[0050] An optical transmitter (OTA) can be configured by connecting an electronic circuit (digital signal processor DSP) that outputs a modulation signal So to the optical modulation device MD to perform modulation operations on the optical modulation device MD. In order to obtain the modulation signal S to be applied to the optical waveguide element, it is necessary to amplify the modulation signal So output from the digital signal processor DSP. For this reason, in Figure 14, a driver circuit DRV is used to amplify the modulation signal. The driver circuit DRV and the digital signal processor DSP can be placed outside the housing CA, but they can also be placed inside the housing CA. In particular, by placing the driver circuit DRV inside the housing, it is possible to further reduce the propagation loss of the modulation signal from the driver circuit. [Industrial applicability]

[0051] As described above, the present invention makes it possible to provide an optical waveguide element that suppresses discharges between electrodes sandwiching the optical waveguide. Furthermore, it makes it possible to provide an optical modulation device and an optical transmission device using the optical waveguide element. [Explanation of Symbols]

[0052] 1. Substrate having pyroelectric effect OW Optical Waveguide EL,EL1~22 Electrode layer P,P1~P22 Protrusion F Optical Fiber CA cabinet MD Optical Modulation Device DRV driver circuit DSP (Digital Signal Processor) OTA Optical Transmitter

Claims

1. An optical waveguide element having a substrate having a pyroelectric effect, a projection extending in a specific direction formed on the surface of the substrate, and an electrode covering at least a part of the projection, On each of the two sides of the projection, the charges generated by the pyroelectric effect are opposite in positive and negative charges. The optical waveguide element is characterized in that the electrodes are arranged to cover the two sides of the protrusion in each electrically connected region.

2. In the optical waveguide element according to claim 1, The substrate has multiple protrusions formed on it, some of which are optical waveguides. The optical waveguide element is characterized in that the electrode is an electrode for applying an electric field to the optical waveguide.

3. In the optical waveguide element according to claim 1, The electrode has a lower electrode positioned in contact with the surface of the substrate and an upper electrode positioned above the lower electrode. An optical waveguide element characterized in that each lower electrode is arranged to cover the two sides of the protrusion.

4. In the optical waveguide element according to claim 1, Including the space between the substrate and the electrode and covering the upper side of the substrate, or including the upper side of the electrode and covering the upper side of the substrate, with a resistivity of 10 ６ ~10 １１ An optical waveguide element characterized by having a conductive film of Ωm thickness.

5. In the optical waveguide element according to claim 1, The electrode is characterized in that, in each electrically connected region, the ratio of the area covering one side of the protrusion to the area covering the other side is within the range of 0.8 to 1.

2.

6. In the optical waveguide element according to claim 1, An optical waveguide element characterized in that the angle of the side surface of the projection with respect to a plane parallel to the surface of the substrate is less than 75 degrees.

7. In the optical waveguide element according to claim 1, The substrate has multiple protrusions formed thereon, with the spacing between adjacent protrusions being in the range of 1 to 20 μm. An optical waveguide element characterized in that the electrode is arranged on at least one of the adjacent protrusions.

8. In the optical waveguide element according to claim 1, The electrode is an optical waveguide element characterized in that the thickness of the electrode positioned on the side of the protrusion is thinner than the thickness of the electrode positioned on the top of the protrusion.

9. The optical waveguide element described in claim 2 is The optical waveguide element is housed within a casing. An optical modulation device characterized by comprising an optical fiber that inputs or outputs an optical wave to the optical waveguide.

10. In the optical modulation device according to claim 9, The optical waveguide element includes a modulation electrode for modulating the light wave propagating through the optical waveguide. An optical modulation device characterized by having an electronic circuit inside the housing that amplifies the modulation signal input to the modulation electrode of the optical waveguide element.

11. The optical modulation device according to claim 9, An optical transmitting device characterized by having an electronic circuit that outputs a modulation signal for causing the optical modulation device to perform a modulation operation.

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